Re: S-expression I/O in Ada

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wccy6ceaaxz.fsf@shell01.TheWorld.com...
> "Randy Brukardt" <randy@rrsoftware.com> writes:
>
>> Not sure if it still exists in the real world, but the compiler we did 
>> for
>> the Unisys mainframes used Stream_Element'Size = 9.
>
> Interesting.  Can these machines communicate with non-Unisys machines
> over a regular TCP/IP network?  E.g. send an e-mail using standard
> protocols, that can be read on a x86?
>
> I assume Storage_Element'Size = 9, too.  Correct?

I think so, although we had tried for a while to use 36 for such things (it 
was a word-addressable machine). But since we were using the C code 
generator, it emulated a 9-bit byte addressable machine for the obvious 
reasons, and eventually we changed to that model, using strong alignments to 
make the code more efficient.

> Next question: Is (was) there any Ada implementation where
> Stream_Element'Size /= Storage_Element'Size?
>
>>...(The Unisys mainframes
>> are 36-bit machines.) Stream_Element'Size = 8 would have made the code 
>> for
>> handling arrays awful.
>>
>> Similarly, Character'Size = 9 on that machine.
>
> That sounds like a non-conformance, at least if the SP Annex
> is supported.  Maybe you mean X'Size = 9, where X is of
> type Character?  You'd certainly want 'Component_Size = 9
> for array-of-Character.

You're probably right. I never implemented Ada 95 'Size because it is 
meaningless. Janus/Ada 'Size is essentially what GNAT calls 'Object_Size, 
and it is used for all allocation/representation decisions in the absence of 
representation clauses. (Indeed, what I intend to do "someday" is covert the 
existing Size code to be reported as Object_Size, following the model of the 
rejected AI on that attribute, and then implement 'Size as mandated by the 
Standard, for no purpose other than matching the legality rules of the 
Standard. (Object_Size would continue to be the significant factor in object 
layout.)

                  Randy.